API changelog

# API changelog

## 2026-05-23 — Stage 2 §7

- Initial publication of the developer portal at `/developers`.
- Canonical schemas for `LeadCreate`, `CalculateInput`, `CalculateResponse`, `RateSheetCreate`, `WebhookLeadReceived`.
- HMAC-SHA-256 webhook signing helper at `lib/api/schemas/webhooks.ts` (single source of truth for the docs sample + the runtime route handlers).
- Documented rate limits: 100 req/min on `/v1/calculate`, 30/min on `/v1/sheets`, 100/min on `/v1/leads`, 10/min on `/v1/leads/list`.

## Unreleased

- `/v1/sheets` and `/v1/leads` route handlers will land alongside the §9 CRM connector work.